1. Field of the Invention
This invention relates to a direct viewing picture image display apparatus for displaying a picture image on the retina of an eye using a laser beam and particularly for displaying a stereoscopic picture image using a laser beam.
2. Description of the Prior Art
Picture image display apparatus which employ a laser beam are already known. One of such picture image display apparatus is a projecting type picture image display apparatus wherein a laser beam emitted from a light source is optically modulated in response to a video signal and then horizontally and vertically scanned by a scanning system, and the thus scanned laser beam is projected to a screen. A characteristic of such apparatus is that a picture image of a high brightness, a high resolution and a high color purity can be achieved with such apparatus.
However, with the picture image display apparatus described above, since a screen has a rough surface, there is a problem that a projected laser beam is diffused, which causes flickering of the laser beam, that is, so-called speckle noises are produced.
Picture image display apparatus of the type mentioned are frequently employed to display a stereoscopic picture image thereon. Various techniques have been developed for such picture image display apparatus and disclosed in various documents including Chihiro Masuda, "Three-Dimensional Display", Industrial Books and "Attempt of Development of Three-Dimensional Display Till Now and Future View", Image Information, August, 1985. Picture images called three-dimensional picture image or stereoscopic picture image are classified into the following three types:
(1) Two-eye type picture image. From the point of view of an amount of information, such picture image has an amount of information for the left and right eyes. Such picture image is called stereoscopic picture image.
(2) A picture image as a reproduction image of a body which looks afloat at a certain location in a space. Thus, if a visual point moves, then a different side face of the picture image can be seen. Such picture image has an amount of information equal to or greater than that for a plurality of eyes. Such picture image is called three-dimensional picture image in a narrow sense.
(3) A picture image which makes use of an optical illusion.
Factors for an image to be recognized as a stereoscopic image are listed in Table 1 annexed hereto. In particular, in the case of viewing with a single eye, focusing, a magnitude of the image, a kinesthetic parallax and a field of view are such factors, and in the case of viewing with two eyes, binocular convergence and a binocular parallax are additional factors. This is disclosed, for example, in Television Society Bulletin, Vol. 43, NO. 8, 1989.
Factors of stereoscopic perception with conventional stereoscopic display apparatus disclosed in the documents mentioned above and so forth are classified appearing in Table 2 also annexed hereto.
Picture image display apparatus for displaying a stereoscopic picture image are also proposed in several patents including, for example, Japanese Patent Laid-Open Application No. 64-42998, Japanese Patent Laid-Open Application No. 62-77794, Japanese Patent Laid-Open Application No. 56-69612 and U.S. Pat. No. 4,799,103.
However, the display apparatus disclosed in Japanese Patent Laid-Open Application No. 64-42998 is disadvantageous in that, since a light emitting body must be caused to emit divergent light, it is difficult to achieve both a high resolution and a sufficient brightness.
Meanwhile, the display apparatus of Japanese Patent Laid-Open Application No. 62-77794 is disadvantageous in that it is difficult to realize the apparatus because a variable focus lens array of a delicate profile must be prepared.
The display apparatus disclosed in Japanese Patent Laid-Open Application No. 56-69612 is disadvantageous in that it is difficult to move a screen at a high speed and besides possible deterioration in picture quality by speckle noises cannot be avoided.
The apparatus disclosed in U.S. Pat. No. 4,799,103 is also disadvantageous in that, since it includes a variable focus mirror, a so-called phantom image phenomenon wherein the inside or the opposite side of a body being displayed can be seen takes place and it is not suitable to display an image of an image signal originating in television broadcasting or the like wherein raster scanning is performed.
Further, it is often the case with regard to any of the display apparatus described above that, since a three-dimensional image is displayed as a real image, it is complicated in construction and requires a large size.